Method and apparatus for making foam

ABSTRACT

An improvement in the manufacture of flexible densified polyurethane foam wherein the partially cured freely risen foam is fed through a crush conveyor to minimize the density gradient throughout the vertical cross section. The crush conveyor includes an upper crushing section which is arcuate and has a radius of a dimension such that the ratio of the radius of the arc to height of the partially cured freely risen foam is 1.1 to 1 or greater. The crush conveyor has a bottom crushing section which may be arcurate with a radius of a dimension such that the ratio of its radius to the height of the partially cured freely risen foam is also 1.1 to 1 or greater. The radius of the bottom arcuate crushing section may be the same or larger than the radius of the top arc. As an alternative, the bottom crushing section may be planar and may be horizontal, or inclined with respect to the horizontal.

BACKGROUND OF THE INVENTION

This invention relates to an improvement in a method and apparatus formaking flexible densified polyurethane foam, and more particularly to amethod and apparatus for crushing the partially cured freely risen foam.

"Crush" as used herein means to compress a cellular material so as topermanently increase the density thereof.

"Curing" as used herein means reaction of a mixture such that apermanent resilient or rigid shape is produced.

"Freely risen foam" as used herein means a foam in which expansion or"rise" due to bubble or "cell" generation has stopped yet curing has notbeen completed.

"Partially cured foam" as used herein means a freely risen cellular foamstructure which has only cured enough that when compressed the foam iscrushed yet retains a cellular structure.

"Densified foam" as used herein means foam that has been produced bycrushing partially cured foam.

In U.S. Pat. No. 3,506,600, issued Apr. 14, 1970 to N. C. Zocco et al,there is disclosed a method of making densified polyurethane foamwherein the partially cured, freely risen foam is crushed between tworotating crusher rollers. After crushing between the crusher rollers,the foam is permitted to completely cure and is cut into predeterminedlengths, either before or after being completely cured. The top andbottom of the foam lengths may, due to the nature of the process, have arelatively thin outer layer of very low density foam which is usuallytrimmed off. Then, depending upon the application, the foam length iseither maintained in its original thickness, or sliced horizontally toprovide a plurality of sheets from one original foam length.

Prior to the present invention, even though extensive efforts have beenmade to optimize the time after the foam has risen and the start of thecrushing or densifying process, the density gradient across the verticalsection remains significantly large. In fact, the density gradient issignificantly large such that the range of densities exceed the normalproduct density tolerance causing more than one product to be producedwhen the foam length is horizontally sliced into a plurality of sheets.The economic implication of this is the production of by-productmaterial which is either not useful or is not needed at the present timeand which requires storage and necessitates an undue buildup ofinventory.

SUMMARY OF THE INVENTION

It has been found that in accordance with the present invention,polyurethane foam can be produced and densified in such a way that thedensity gradiant through a given cross section is reduced and theby-product material is minimized.

More specifically, it has been found that densified polyurethane foamscan be prepared by allowing a polyurethane foam forming reaction mixtureto rise thereby forming a partially cured, free risen cellular material.The partially cured cellular material has a compressive force applied toit by means of a crush conveyor having an upper arcuate crushing sectionof a radius such that the ratio of the radius to the free-rise height ofthe partially cured foam is at least 1.1 to 1 or greater. The crushconveyor also includes a bottom crushing section which may be arcuatewith a radius of a dimension such that the ratio of the radius to thefree-rise height of the partially cured foam is also 1.1 to 1 orgreater. The bottom crushing section may have a radius the same as orgreater than the top crushing section.

As an alternative, the bottom crushing section may be planar and may behorizontal or inclined with respect to the horizontal.

DESCRIPTION OF THE DRAWINGS

The present invention may be more readily understood by reference to thefollowing description of various embodiments of the present inventionand to the accompanying drawing in which:

FIG. 1 is a side view partially in section of a crush conveyor mechanismfor use in practicing the present invention;

FIG. 2 is a plot of the standard deviation of the density gradient fromthe average density of various foam samples for different averagedensities and showing data for samples produced according to the knownprocess and data for samples produced according to an embodiment of thepresent invention;

FIG. 3 is a graph plotting the density versus the depth of a sample, thesample being prepared according to one embodiment of the presentinvention; and

FIG. 4 is a graph plotting density versus the depth of a sample, thesample being prepared according to the known process.

The present invention is particularly applicable to the continuousprocess of producing densified polyurethane foam. In the typicalprocess, the foam-forming ingredients are admixed in a suitable mixinghead and the resulting mixture fed to a moving conveyor having suitableside-retaining means to contain the liquid reactant. The side-retainersare necessary until the foam gels sufficiently to support its ownweight. As the reaction proceeds while moving along the conveyor,bubbles or "cells" form in the reaction mixture which affects a volumeincrease and the formation of an uncured cellular porous gel. After theuncured cellular porous gel has traveled along the conveyor for apredetermined period of time, the partially cured freely risen foam 1 ispassed to a crush conveyor mechanism 2 such as shown in FIG. 1. Thepartially cured, freely risen cellular foam has a height H₁ prior tocrushing.

As shown in FIG. 1, the crush conveyor mechanism 2 may include upper andlower drive rollers 4 and 6 respectively which are journaled at each endto suitable support brackets 8 and 10. The lower support brackets 10 aremounted on vertically extended support poles 12 and 14, pole 14 beingpositioned behind pole 12 in the view shown in FIG. 1. While FIG. 1 onlyshows the right-hand end of the brackets 8 and 10 being mounted to asupport pole 12, it is to be understood that the left-hand ends may alsobe supported by a set of poles if desired.

The support poles 12 and 14 include upper telescoping sections 16 and 18to which the right-hand end of the upper support brackets 6 areattached. Section 18 is positioned behind section 16 as shown in FIG. 1.If a second set of poles are used to support the left-hand end of thebrackets 10, such poles should also be provided with telescopingsections to support the left-hand end of the brackets 8.

Mounted to and extending downwardly from each support bracket 8 is asupport arm 20. An upperly extending support arm 22 is attached to eachof the lower support bracket 10.

A second set of support poles 24 and 26 is provided at a point upstreamfrom support poles 12 and 14. A set of horizontally opposed, upperroller supporting brackets 28 and 30 have their downstream end attachedto the free end of support arm 20 by a pivot pin 32. The upstream end ofeach of the upper roller supporting brackets 28 and 30 is positioned onthe inside of its respective support pole 24 and 26 and is pivotallyattached by means of a U-Bolt 34 surrounding a pivot pin 36. The U-bolt34 is attached to a bracket 38 which in turn is attached to itsrespective pole 24 or 26.

A set of horizontally opposed lower roller supporting brackets 40 and 42have their downstream ends attached to the free end of the support arms22. The upstream end of each lower roller supporting bracket 40 and 42is positioned on the inside of its associated pole 24 or 26 and isattached thereto by any suitable means such as the pin bracket, andU-bolt arrangement used in connection with the upper roller supportingbrackets 28 and 30.

A series of upper rollers 44 extend between the set of upper rollerssupport members. Similarly, a set of bottom rollers 46 extend betweenthe two lower roller support members. According to the embodiment shownin FIG. 1, the bottom rollers 46 define a path which is generally flatand inclined upwardly toward the downstream end of the conveyor 2 and adownstream flat horizontal portion. The upper rollers 44 are spaced fromthe lower rollers in such a manner as to provide crushing section 48 ofa predetermined height H₂ to provide the desired average density, and adownstream discharge section 50.

An upper conveyer belt 52 extends about the drive roller 4, under anidler roller 54, over an idler roller 56 and back to the drive roller 2.In like manner, a lower conveyor belt 58 extends around the drive roller6, over an idler roller 60, over idler roller 62 and back to the driveroller 6.

Both the upper and lower conveyor belts 52 and 58 have sufficient slacksuch that when the partly cured freely risen cellular polyurethane foamenters the conveyor mechanism 2, the conveyor belts 52 and 58 are pushedagainst the rollers 44 and 46 and the belts 52 and 58 assume the path ofthe rollers heretofore mentioned.

More in detail, the conveyor mechanism 2 includes an upper arcuratecrushing portion 64 which is disposed opposite a flat inclined bottomcrushing portion 66. The arcurate section has a radius "R" which is of adimension such that the ratio of the arc radius to the free-rise heightof foam is greater than 1.1 to 1 and preferably greater than 2 to 1.Although the ratio of arc radius of the upper crushing section to freelyrisen foam height may be theoretically as large as desired, thepreferred operating range is a ratio of between about 2 to 1 to about10.5 to 1.

The angle of incline of the planar bottom crushing section may vary frombeing horizontal up to about 10°, although 6° or less is preferred. Theincline may be upwardly or downwardly toward the downstream end.

As an alternative embodiment, the bottom crushing section 66 may bearcuate in a manner similar to the top crushing section 64. The radiusof the arc should be sufficiently large to provide a ratio of the radiusof the arc to the freely risen height of the foam which is greater than1 to 1 and preferably greater than 2 to 1. If an arcuate crushingsection is used for the bottom crushing section 66, the radius of thebottom arc may be the same as or greater than the radius of the topcrushing section 64.

In the preparation of densified urethane foam using this invention,either the so-called "one-shot method" or the "semi-prepolymertechnique" ("quasi-prepolymer") may be employed. Any combination ofpolyols, including polyether polyols and polyester polyols, organicpolyisocyante, foaming agent, catalyst and other reactants capable offorming a flexible urethane foam can be employed in carrying out theprocess of this invention, and the term "polyurethane foam formingreaction mixture" in the specification and claims herein is meant toinclude any such combination. Typical formulations are described in U.S.Pat. No. 3,072,582, issued Jan. 8, 1963 and Canadian Pat. No. 705,938,issued Mar. 16, 1965.

While, as indicated above, both polyether and polyester polyols can beemployed in the practice of this invention, preferred embodimentsutilize the polyether polyols in the preparation of the polyurethanefoam forming reaction mixture. To further illustrate suitableformulations, the polyether polyols, useful for the preparation of thepolyurethane foams, include oxyalkylated polyhydric alcohols having amolecular weight in the range between about 700 and about 10,000 andpreferably between about 1,000 and 6,000. The hydroxyl number of thepolyether polyol is generally less than about 250 and preferably in therange between about 25 and about 175. These oxyalkylated polyhydricalcohols are generally prepared by reacting in the presence of analkaline catalyst, a polyhydric alcohol and an alkylene oxide such asethylene oxide, propylene oxide, butylene oxide, amylene oxide,epichlorohydrin, and mixtures of these alkylene oxides, by either randomaddition or step-wise addition.

Polyhydric alcohols suitable for use in preparing the polyether polyolinclude ethylene glycol, pentaerythritol, methyl glucoside, propyleneglycol, 2,3-butylene glycol, 1,3-butylene glycol, 1,5-pentane diol,1,6-hexane diol, glycerol, trimethylolpropane, sorbitol, sucrose,mixtures thereof and the like. If desired, a portion or all of thepolyhydric alcohol may be replaced with another compound having at leasttwo reactive hydrogen atoms, such as alkyl amines, alkylene polyamines,cyclic amines, amides, and polycarboxylic acids. Suitable alkyl aminesand alkylene polyamines include methylamine, ethylamine, propylamine,butylamine, hexylamine, ethylenediamine, 1,6-hexanediamine,diethylenetriamine, and the like. Also, such cyclic amines aspiperazine, 2-methylpiperazine and 2,5-dimethylpiperazine can also beused. Amides, such as acetamide, succinamide and benzenesulfonamide,constitute a further class of such reactive hydrogen compounds. A stillfurther class of such reactive hydrogen compounds is the di- andpolycarboxylic acids, such as adipic acid, succinic acid, glutaric acid,aconotic acid, diglycollic acid, and the like. It will be recognizedthat the reactive hydrogen compound can be one containing differentfunctional groups having reactive hydrogen atoms, such as citric acid,glycollic acid, ethanolamine, and the like. Aromatic polyamines such astoluene diamine can also be employed. Mixtures of oxyalkylatedpolyhydric alcohols are also suitable for use in the process of thisinvention.

The organic polyisocyanates used in the preparation of the polyurethanefoams include toluene diisocyante, such as the 4:1 mixture or the 65:35mixture of the 2,4- and 2,6-isomers, ethylene diisocyante, propylenediisocyanate, methylene-bis-4-phenyl isocyante,3,3'-bitoluene-4,4'-diisocyante, hexamethylene diisocyante,naphthalene-1,5-diisocyante, polyphenylene polymethylene isocyanate,mixtures thereof and the like. The amount of isocyanate employed in theprocess of this invention should be sufficient to provide at least about0.7 NCO group per hydroxyl group present in the reaction system, whichincludes the polyol as well as any additive or foaming agent employed.An excess of isocyanate compound may be conveniently employed; however,this is generally undesirable due to the high cost of the isocyanatecompounds. It is preferable, therefore, to employ sufficient isocyanateto provide no greater than about 1.25 NCO groups per hydroxyl group, andpreferably between about 0.9 and about 1.15 NCO groups per hydroxylgroup. The ratio of NCO to OH groups times 100 is referred to as the"index".

The partially cured polyurethane foams are prepared in the presence of afoaming agent, reaction catalysts, and preferably a small proportion ofa conventional surfactant. The foaming agent employed may be any ofthose known to be useful for this purpose, such as water, as well asorganic foaming agents containing up to about seven carbon atoms such asthe halogenated hydrocarbons, lower molecular weight alkanes, alkenes,ethers and mixtures thereof. Typical halogenated hydrocarbons include,but are not limited to: monofluorotrichloromethane,dichlorofluoromethane, difluorodichloromethane,1,1,2-trichloro-1,2,2-trifluoroethane, dichlorotetrafluoroethane, ethylchloride, methylene chloride, chloroform, and carbon tetrachloride.Other useful foaming agents include lower molecular weight alkanes,alkenes and ethers such as methane, ethane, ethylene, propane,propylene, pentane, hexane, heptane, ethyl ether, diisopropyl ether,mixtures thereof, and the like. The amount of foaming agent employed maybe varied within a wide range. Generally, however, the halogenatedhydrocarbons are employed in an amount from about 1 to 50 parts byweight per 100 parts by weight of the polyol, and generally water isemployed in an amount from about 1.0 to 6.0 parts by weight per 100parts by weight of the polyol.

The polyurethane foams are prepared in the presence of a catalyticamount of a reaction catalyst. The catalyst employed may be any of thecatalysts known to be useful for this purpose, or mixtures thereof,including tertiary amines and metallic salts, particularly stannoussalts. Typical tertiary amines include, but are not limited to, thefollowing: N-methyl morpholine, N-hydroxyethyl morpholine, triethylenediamine, triethylamine and trimethylamine. Typical metallic saltsinclude, for example, the salts of antimony, tin and iron, e.g.,dibutyltin dilaurate, stannous octoate, and the like. Any catalyticproportion of catalysts may be employed. Preferably, a mixture of amineand metallic salt is employed as the catalyst. The catalyst or catalystmixture, as the case may be, is usually employed in an amount rangingbetween about 0.05 and about 1.5, and preferably between about 0.075 andabout 0.50 percent by weight of the polyol.

It is preferred in the preparation of the polyurethane foams to alsoemploy minor amounts of a conventional surfactant in order to furtherimprove the cell structure of the polyurethane foam. Typical of suchsurfactants are the silicone oils and soaps, and thesiloxane-oxyalkylene block copolymers. U.S. Pat. No. 2,834,748 and T. H.Ferrigno, Rigid Plastic Foams (New York: Reinhold Publishing Corp.,1963),p. 38-42, disclose various surfactants which are useful for thispurpose. Generally up to 2 parts by weight of the surfactant areemployed per 100 parts of the polyol.

Various additives can be employed which serve to provide differentproperties, e.g., fillers such as barytes, clay, calcium sulfate, orammonium phosphate may be added to lower cost and improve physicalproperties. Ingredients such as dyes may be added for color, and fibrousglass, asbestos, or synthetic fibers may be added for strength. Inaddition, plasticizers, deodorants and anti-oxidants may be added. Also,a phosphorous containing burning rate retardant such as tetrakis(2-chloroethyl) ethylene disphosphate or tris (dichloroprophyl)phosphate may also be added.

In practicing the present invention, the polyurethane foaming reactionmixture comprising the above described ingredients is fed to a suitablereaction zone such as by pouring onto a moving conveyor belt where thereaction proceeds. The foaming reaction is exothermic and auxiliary heatis not needed to affect the reaction though it can, of course, beemployed. After the reactants have been admixed for a period of aboutbetween 0.1 and about 20 seconds, an emulsion or cream forms. As thetemperature increases from the reaction, gas bubbles are generated whichcause the formation of an uncured cellular gel material which graduallyincreases in volume.

After generation of gas bubbles is completed, the rise of the uncuredcellular gel material stops. At this point, the method and apparatusaccording to the teaching of the present invention is employed toprovide densified foam compositions.

The period of time which elapses between the completion of the rise ofthe uncured cellular foam and the first application of pressure to thepartially cured foam to affect crushing of the foam (hereinafterreferred to as "crush time") may vary. Generally, it is desirable thatthe "crush time" be from about 0 to about 10 minutes and preferably fromabout 0 to about 6 minutes. Although flexible densified polyurethanefoams can be provided immediately after completion of the rise,practical operations require at least about 6 seconds to elapse prior tocrushing.

It has also been found desirable to maintain the temperature of theambience during crushing within certain limits which is related to"crush time". In the case where the "crush time" is between about 0 and2.5 minutes, temperatures between about 45° and about 200° F. andpreferably between 45° and about 100° F. may be employed. Narrowertemperature ranges may be utilized when the partially cured cellularmaterial is maintained for a longer "crush time". Thus, when the timeinterval is between 2.5 and about 5 minutes, temperatures between about45° and 200° F. and preferably between about 45° and 100° F. may bemaintained, while temperatures between about 45° and 110° F. andpreferably between 45° and about 85° F. may be employed for "crushtimes" of about 5 to about 10 minutes.

Conventional means such as ovens and cooling systems may be employed asnecessary to provide the desired temperatures. In commercial operationsit is particularly preferred to operate under environmental conditionsand thus temperatures from about 70° to about 110° F. are employed whilemaintaining the "crush time" within the broad range of 0 to 10 minutes.

At the end of the "crush time", the partially cured polyurethane foam iscompressed by the apparatus and method described above. The degree ofdeflection necessary to provide good densified foams may vary dependingupon the desired average density. It has been found desirable tocompress the partially cured cellular material to between about 2/3 and1/10 of its original thickness after rise. The greater the degree ofdeflection, the greater will be the average density of the crushed or"densified" foam.

The desired degree of compression may be achieved by adjusting theopening H₂ between the upper and lower crushing portions 64 and 66 ofthe apparatus shown in FIG. 1. This may be accomplished by moving thetelescoping poles 16 and 18 in a vertical direction permitting the upperroller mounting brackets 28 and 30 to pivot about pivot pin 36.

After the partially cured polyurethane foam has been subjected tocompression by the crushing conveyor 3, the curing of the compressedmaterial may be completed. While curing can be accelerated by theapplication of heat, such treatment is not necessary since the foam willcompletely cure under ambient conditions.

After removal of the compressing force and completion of the curing, thedensified foam may recover a small portion of the difference between itsinitial height and the crushing gap. The degree of recovery depends uponthe particular process variables. If the foam has been densified, it isapparent that it will never regain its original dimensions.

The following examples are presented to illustrate the invention morefully without any intention of being limited thereby.

A polyurethane foam forming reaction mixture was prepared from thefollowing ingredients in the indicated proportions:

    ______________________________________                                        Ingredients:            Parts by weight                                       ______________________________________                                        Oxypropylated glycerin (Moleculor                                             weight 3000)            100                                                   Toluene diisocyanate (80/20, 2,4/2,6                                          isomer mixture; 110 index)                                                                            47.8                                                  Water                   3.6                                                   Silicone surfactant (Dow Corning                                              DC-190')                1.0                                                   Amine catalyst (33% solution of triethylene                                   diamine in diprophylene glycol)                                                                       .25                                                   Stannous octoate        .5                                                    Tris (dichloropropyl) phosphate                                                                       10                                                    ______________________________________                                         'This surfactant is a block copolymer of a polydimethylsiloxane and a         polyether resin.                                                         

The above reaction mixture, which had a free rise density ofapproximately 1.66 pcf (pounds per cubic foot) were utilized to preparea series of lengths of partially cured, fully risen foam, by pouring asufficient amount of the mixture at a sufficient rate onto a movingconveyor to provide a free rise height of approximately 45 inches foreach sample. A first set of the samples was conveyed to and passedbetween two 8 foot diameter crush rollers spaced apart varying amountsto provide samples having an average density of between 2.8 and 5 pcf.The two 8 foot diameter crush rollers represent the prior art technique.The actual density was calculated at various points from top to bottomacross the vertical axis of the sample to obtain the density gradient.The standard deviation of these densities with the average sampledensity was calculated. This gradient standard deviation provides anindication of the density gradient range which should be as small aspossible. The dark data points in FIG. 2 show the gradient standarddeviation plotted for a range of average densities for samples crushedbetween 8' diameter crush rollers.

A second set of samples was conveyed to a crush conveyor mechanism ofthe type shown in FIG. 1 wherein the top crushing section had a radiusof 10 feet and the bottom crushing section was planar and inclinedupwardly from the horizontal 4°. The minimum height H₂ of the crushingsection, (crush height) was varied to provide samples having averagedensities between about 2 and about 5 pcf. The standard deviation of thedensity of each sample at various points across the vertical axis withthe average sample density was calculated. The light data points in FIG.2 show the gradient standard deviation plotted for a range of averagedensities for these samples.

As can be seen from the graph of FIG. 2, the samples crushed between a10 foot radius top arc and flat inclined bottom exhibited a lowergradient standard deviation than did the samples crushed between two 8foot diameter crush rollers. As the height of the partially curedsamples in all cases was approximately 45 inches, the ratio of the arcradius to foam height for the 20 foot diameter top roll was 2.67. In thecase of the 8 foot diameter crush rolls, the ratio of arc radius topartially cured, fully risen foam height was 1.07. The graph of FIG. 2thus indicates that the density gradient of the foam produced using aconveying mechanism according to the present invention as compared tothat produced by previous practice was substantially lower, especiallyin the lower average density ranges.

Another foam forming reaction mixture was prepared similar to that setforth above with the exception that four parts by weight of Tetrakis(2-chloroethyl) ethylene diphosphate was used in place of the 10 partsby weight of Tris (dichloropropyl) phosphate. A foam sample was preparedby pouring the foam forming reaction mixture onto a moving conveyor toprovide partially cured, fully risen foam sample having a height ofabout 27 inches. The sample was conveyed to a crush conveyor mechanismof the type shown in FIG. 1 having a top arcuate crushing member of 11foot radius and a bottom crushing mechanism of arcuate shape having a 22foot radius. The crush opening H₂ was 11 inches. The sample, aftercrushing, regained a portion of its height, having a final height of14.5 inches. The density of the sample was ascertained at 0.5 inchintervals across its vertical cross-section. The density at the varioussample depths is shown plotted in FIG. 3. The average density of thesample was 2.66 pounds per cubic foot.

The same foam forming reaction mixture used in connection with FIG. 3was poured onto a moving conveyor to provide a sample having a height ofabout 26 inches. The fully risen sample, before being completely cured,was transported to a pair of crush rollers each of which had a radius of2 feet. The crush opening was 11 inches. After crushing and curing, theheight of the foam sample was 14 inches and had a density of 2.64 pcf.The density at various sample depths were ascertained and plotted inFIG. 4.

As can be noted from the comparison of FIGS. 3 and 4, the sample usingthe crush conveyor mechanism with a top arc of 11 foot radius and bottomarc of 22 foot radius had a generally flatter curve, and thus lessvariation in density, than did the sample crushed between the 4 footdiameter crush rollers.

Another series of samples were prepared utilizing the foam formingreaction mixture used in connection with the examples of FIGS. 3 and 4.These samples were crushed between either crush rollers, or a crushconveyor mechanism having various arc radii to freely risen foam heightratio as indicated in Table 1. The average sample density and densitygradient standard deviation were calculated. As will be seen from Table1, for a given average sample density, the utilization of the crushconveyor mechanism wherein the arc radius to sample height ratio hasbeen increased over that previously used, resulted in a lower densitygradient standard deviation, indicating that the foam so produced had amore uniform density.

                  Table 1                                                         ______________________________________                                        Top         Bottom    Avg.                                                    Arc radius/ Arc radius/                                                                             Sample   Density Gradient                               foam height foam height                                                                             Density  Standard Deviation                             ______________________________________                                        1.   .92        .92       2.4    .6                                                (Old Process)        3.0    .5                                                                     4.0    .35                                                                    5.0    .2                                           2.   5.1        5.1       2.4    .32                                                                    3.0    .26                                                                    4.0    .19                                                                    5.0    .15                                          3.   5.1        10.2      2.4    .29                                                                    3.0    .23                                                                    4.0    .17                                                                    5.0    .15                                          4.   5.1        Flat      2.4    .23                                                                    3.0    .21                                          ______________________________________                                    

As the examples point out, the increased radius of the upper crushingportion used in conjuction with a bottom crushing portion having eitheran increased radius or planar configuration, results in lower densitygradients as compared with the conventional process. Without any intentto be bound hereby, it is theorized that the large density gradientproduced by the convention process is the result of horizontal shearforces evolving from a large ratio of vertical crush distance tohorizontal travel of the foam. The present invention reduces this ratiothrough the provision of a crush conveyor utilizing a crushing portionof a relatively large arc.

What is claimed is:
 1. In an apparatus for making flexible densifiedpolyurethane foam wherein a cellular polyurethane foam-forming reactionmixture is allowed to rise and is crushed before being completely cured,the improvement comprising crush conveyor means for crushing saidpartially cured freely risen cellular foam as said foam is beingconveyed, said conveyor means including an upper crushing portion ofarcuate configuration having a radius of a dimension such that the ratioof the arc radius to height of the freely risen foam is greater than2.67 to 1, and a bottom crushing portion oppositely disposed from theupper crushing portion, said bottom crushing portion comprising a planarsection and the final foam density is under about four pounds per cubicfoot.
 2. The apparatus of claim 1 wherein said bottom crushing sectionis inclined upwardly toward the downstream end of the conveyor means. 3.The apparatus of claim 2 wherein said bottom crushing section isinclined less than 10°.
 4. The apparatus of claim 1 wherein said ratiois between under about 10.5 to
 1. 5. In an apparatus for making flexibledensified polyurethane foam wherein a cellular foam-forming mixture isallowed to rise and is crushed before being completely cured, theimprovement comprising crush conveyor means for crushing said partiallycured cellular freely risen foam as said foam is being conveyed, saidconveyor means including an upper crushing portion of arcuateconfiguration having a radius of a dimension such that the ratio of thearc radius to the height of the freely risen foam is greater than 2.67to 1, and a bottom crushing portion being of an arcuate configurationhaving a radius of a dimension such that the ratio of arc radius to theheight of the freely risen foam is greater than 1.1 to 1 and the finalfoam density is under four pounds per cubic foot.
 6. The apparatus ofclaim 5 wherein said ratio of said bottom crushing portion is greaterthan said ratio of said upper conveyor portion.
 7. The apparatus ofclaim 5 wherein said ratio of said upper crushing portion is under about10.5 to
 1. 8. The apparatus of claim 5 wherein said ratio of said lowercrushing portion is between about 2 to 1 and about 10.5 to
 1. 9. In aprocess for making flexible densified polyurethane foam wherein acellular polyurethane foam-forming reaction mixture is allowed to riseand is crushed before being cured, the improvement comprising conveyingsaid cellular partially cured freely risen foam to a crush conveyor andcrushing said foam as said foam is being conveyed between upper andlower crushing portions of said crush conveyor, said upper crushingportions of said crush conveyor, said upper crushing portion being ofarcuate configuration having a radius of a dimension such that the ratioof the arc radicus to the height of the freely risen foam is greaterthan 2.67 to 1, the lower crushing portion being oppositely disposedfrom said upper portion and comprising a planar section and the finalfoam density is under 4 pounds per cubic foot.
 10. In the method ofclaim 9, said bottom crushing section being inclined with respect to thehorizontal.
 11. In the method of claim 9 said bottom crushing sectionbeing inclined less than 10°.
 12. In the method of claim 9, said ratiobeing under about 10.5 to
 1. 13. In a process for making flexibledensified foam wherein a cellular polyurethane foam-forming reactionmixture is allowed to rise and is crushed before being cured, theimprovement comprising conveying said partially cured freely risen foamto a crush conveyor and crushing said foam as said foam is beingconveyed between upper and lower crushing portions of said crushconveyor, said upper crushing portion being of arcuate configurationhaving a radius of a dimension such that the ratio of the arc radius tothe height of the freely risen foam is greater than 2.67 to 1, and saidbottom crushing poriton being oppositely disposed from said upperportion and being of an arcuate configuration having a radius of adimension such that the ratio of arc radius to the height of the freelyrisen foam is greater than 1.1 to 1, the foam product density is underabout 4 pounds per cubic foot.
 14. In the process of claim 13, saidratio of said lower crushing portion being greater than said ratio ofsaid upper crushing portion.
 15. In the process of claim 13, said ratioof said upper crushing portion being under about 10.5 to
 1. 16. In theprocess of claim 13, said ratio of said lower crushing portion beingbetween about 2 to 1 and about 10.5 to 1.